Conventionally, as a planar light source used in a backlight of a liquid crystal display device or in an illuminated signboard, there is a planar light source using a three-dimensional light reflection plate made from synthetic resin. As a light reflection plate such as this, for example, a light reflection plate formed as follows is proposed (refer to, for example, Patent Literature 1). In the light reflection plate, a linear bending line that is a perforated line, a pressed ruled line, a half-cut, or the like is formed on a foamed plastic film or sheet that reflects light, and a chevronwise section is formed by the film or sheet being bent along the bending line.    Patent Literature 1: Japanese Patent Laid-open Publication No. 2004-138715